The purpose of this study is to extend our prior work in understanding the risk structure of hospital readmissions and the impact of post-operative services for patients with joint replacement surgery on their physical functioning. We propose to take advantage of a unique patient-specific data sources (the Health and Retirement Study (HRS) and the National Health and Aging Trends Study (NHATS) both linked to Medicare claims data for patient-level measures of functional status, mobility limitations and social support to enhance current claims- data based risk models for both hospital readmissions and to understand the impact of different post-operative services on subsequent physical functioning. Using statewide Medicare claims data, we will also explore the use of census-derived variables that could serve as surrogate measures of the HRS and NHATS variables of functional status, mobility and social support that could be readily implemented as enhancements to nationwide claims data. Finally, we propose to study the impact of the ?bundle? of services provided during the CMS defined post operative period and the effect those services have on patients' measured physical function. Our goal remains to protect vulnerable patients and the hospitals they frequent while providing the correct value signal to the health system.